1. Field of the Invention
The present invention relates to a gray shade displaying device and a method for displaying gray shades being suitable for use in an LCD (liquid crystal display) to display a color image in multiple shades of gray on a display of a computer, TV or the like.
2. Description of the Related Art
The LCD is now in increasing demand and further being developed rapidly, instead of a CRT (Cathode Ray Tube), for reasons that it does not occupy a large area for its installation, consumes power little and has little adverse effect on a human body.
In particular, a DSTN (Dual Supper Twisted Nematic)-type or STN (Super Twisted Nematic)-type LCD (hereinafter referred to simply as an xe2x80x9cSTN-LCDxe2x80x9d) is increasing popular, among manufacturers, as a means of displaying images which can be designed or manufactured at a low cost.
Paralleling the widespread use of the LCD, the need for displaying a variety of varicolored images using gray-scale colors is increasing in the field of display technology for a computer or the like.
One pixel (color element) forming the LCD screen is represented by two values, one for a xe2x80x9clight statexe2x80x9d and the other for a xe2x80x9cdark statexe2x80x9d and, therefore, the gray-scale color can not be displayed by one pixel. To solve this problem, in a TFT (Thin Film Transistor)-type LCD which reacts quickly to a signal, by changing a ratio of time (i.e., duty ratio) between the light and dark states taken by one pixel, images can be displayed in multiple shades of gray.
However, such a method as used in the TFT-type LCD cannot be applied to the STN-LCD due to its slow reaction to a signal. In general, therefore, a method is adopted where one dot forming an image is composed of two or more pixels. For example, to display an image in 4 shades of gray, one dot is composed of 4 pixels and the number of pixels for the xe2x80x9clightxe2x80x9d state is changed depending on shades of gray to be displayed.
Conventionally, the STN-LCD for displaying images in multiple shades of gray is provided with a LCD controller to perform the processing described above.
FIG. 10 is a block diagram showing configurations of a conventional LCD controller used to display an image on an STN-type or DSTN-type color LCD panel. As shown in FIG. 10, the conventional LCD controller is comprised of an image memory interface 101, a color data determining section 102, a frame rate controlling section 103, a display control signal outputting section 104 and a pattern recognizing section 105. The image memory interface 101 is adapted to derive an image signal from the image memory. The color data determining section is used to produce color data for each of RGB (Red, Green and Blue colors, three primaries) colors using the image signal derived through the image memory interface. The frame rate controlling section is used to display data for an LCD panel based on color data outputted from the color data determining section 102. The frame rate controlling section is also used to output display data for displaying gray shades and is provided with two or more gray shade registers (not shown) into which gray shade data corresponding to each color data is stored. The display control signal outputting section 104 is used to generate timing signals to display an image on the LCD panel in accordance with the display data. The pattern recognizing section 105 is used to output a pattern recognizing signal to indicate a position of a display pixel on the LCD panel.
The LCD panel has only a capability of displaying 2 values, one for a state of lighting and the other for a state of going off, in terms of its principles. To display an image in a shade of gray on the STN-type or DSTN-type color LCD panel, a method is available where one dot forming an image is composed of two or more pixels.
FIGS. 11A to 11C are explanatory views showing one example of methods for displaying gray shades on the LCD panel.
In FIGS. 11A to 11C, one dot is composed of 4 pixels and the gray shade is expressed by changing the number of pixels being in a state of lighting (a diagonally shaped area shows that the pixel is in a state of going off and a hollow portion showing that the pixel is in a state of lighting). That is, FIG. 11A shows that one dot is turned off or is in a state of going off while FIG. 11C showing that one dot is turned on or in a state of lighting. FIG. 11B is an example of displaying of a gray-scale color.
Hereinafter, by taking the case of displaying 4 shades of gray as an example, operations of a conventional gray shade display using the LCD controller shown in FIG. 10 are described.
FIG. 12 is a flowchart indicating one example of flows of processing by the LCD controller used in the conventional gray shade displaying device.
First, the frame rate controlling section 103 selects a gray shade register corresponding to color data for each of R, G and B colors outputted from the color data determining section.
FIG. 13 is an explanatory diagram showing a gray shade register selected in accordance with each color data. The gray shade register is provided to correspond to color data. In the case of displaying 4 shades of gray, for example, as shown in FIG. 13, 2 bits of data is required for the color data and one gray shade register corresponding to color data is selected out of 4 (22) gray shade registers.
The gray shade register for each of the RGB colors may be provided independently or one gray shade register may be used in common for the RGB colors.
Next, the frame rate controlling section 103 selects a specified frame rate controlling pattern in accordance with the pattern recognizing signal indicating a position of the display pixel on the LCD panel (Step St2). The pattern recognizing signal outputted from the pattern recognizing section 105 is a signal indicating the position of the display pixel, which is represented by pixel values (x, y). The pattern recognizing signal outputted from the pattern recognizing section 5 is a signal indicating a position of a display pixel, which is represented by pixel values (x, y).
FIG. 14 is an explanatory view showing a relationship between each color element (dot) forming an image and the pixel values, which presents an image being 640 dots wide and 480 dots long.
As shown in FIG. 14, assuming that values existing at the upper-left portion on the image are (0, 0), values (1, 0) . . . (638, 0) and (639, 0) are disposed toward the right portion on the image and values (0, 1) . . . (0, 478) and (0, 479) are disposed downward on the image.
At this point, the frame rate controlling section 103 is adapted to select either of a frame rate controlling pattern A or B in accordance with low order 1 bit of the values x and y described above.
FIG. 15 is an explanatory view showing which frame rate controlling pattern, A or B, is selected by the frame rate controlling section 103 in accordance with values x and y (low order 1 bit).
FIGS. 16A and 16B are explanatory views showing contents of the frame rate controlling pattern A and B to be selected by the frame rate controlling section 103 respectively. In the case of the frame rate controlling pattern A, if the frame function is zero (0), the 0-th bit of the gray shade register is used for displaying and, similarly, if the frame function is 1, 2, or 3, the 1-st, 2-nd or 3-rd bit of the gray shade register are used for displaying. On the other hand, in the case of the frame rate controlling pattern B, if the frame function is zero (0), the 1-st bit of the gray shade register is used for displaying and similarly if the frame function is 1, 2 or 3, the 2-nd, 3-rd or 0-th bit are used for displaying as well.
Next, the frame rate controlling section 103 is adapted to set data which corresponds to a value of a frame function, selected out of data stored in the gray shade register selected by Step St1 in accordance with the frame rate controlling pattern selected by Step St2.
The frame function represents a function to be added each time one piece of a screen (i.e., one frame) of the LCD panel is filled with images. The frame rate controlling pattern is a pattern set in advance arbitrarily at the time of designing and, if the gray shade register contains 4 bits of data, 2 patterns are set as shown in FIGS. 16A and 16B. In the frame rate controlling pattern A shown in FIG. 16A, if the frame function is, for example, xe2x80x9czero (0)xe2x80x9d, bit 0 is selected for the gray shade register while if the frame function is xe2x80x9c3xe2x80x9d, bit 3 is selected for the gray shade register.
Similarly, in the frame rate controlling pattern B shown in FIG. 16B, if the frame function is, for example, xe2x80x9czero (0)xe2x80x9d, bit 1 is selected for the gray shade register while if the frame function is xe2x80x9c3xe2x80x9d, bit 0 is selected for the gray shade register.
In Step St3 described above, data (1 bit of data) of the gray shade register selected by the frame rate controlling section 103 is outputted as display data for each of the RGB colors on the LCD panel.
In the conventional LCD controller described above, if the number of bits of color data is xe2x80x9cnxe2x80x9d, 2n gray shade registers being 2n bits long are required.
FIG. 17 is an explanatory view showing an ideal gray shade registers being able to be applied to the LCD controller described above. As shown in FIG. 17, registers designed specifically for use for each of the RGB colors and driving circuits having the number corresponding to these registers may be provided.
However, when many gray shade registers and driving circuits are provided within the LCD device, a problem occurs that power consumption is increased. Moreover, increased size of circuits causes a rise in costs as well.
It is apparent that the use of such LCDs as are costly and consume much power for recently-available portable devices including a portable phone or the like using a battery as its main power source causes the depreciation of values of such products.
In view of the above, it is an object of the present invention to provide a gray shade displaying device and a method of displaying gray shades wherein its circuit configurations can be simplified, thus reducing power consumption and related costs and allowing values of products using the device and method to be maintained high.
According to a first aspect of the present invention, there is provided a gray shade displaying device comprising:
a color data determining means to determine color data corresponding to given image data;
a pattern recognizing means to provide a display pattern corresponding to the color data and to decide shades of gray corresponding to color elements for RGB (red, green and blue) colors to which the determined color data belongs; and
a frame rate controlling means to decide gray shade data providing a specified shade of gray by giving frame rate control to the color data and to decide a frame function to which each color element is allocated,
whereby the pattern recognizing means has an extension register to decide whether an intermediate gray shade is displayed or not.
According to a second aspect of the present invention, there is provided a gray shade displaying device comprising:
a color data determining means to determine color data corresponding to given image data;
a pattern recognizing means to provide a display pattern corresponding to the color data and to decide shades of gray corresponding to color elements for RGB (red, green and blue) colors to which the determined color data belongs; and
a frame rate controlling means to decide gray shade data providing a specified shade of gray by giving frame rate control to the color data and to decide a frame function to which each color element is allocated,
whereby the frame rate controlling means has an extension register to decide whether an intermediate gray shade is displayed or not.
In the foregoing, a preferable mode is one wherein it is provided with N bits of gray shade registers each giving a different display pattern and wherein an intermediate gray shade is displayed in N shades of gray by using data contained in the gray shade register providing a higher shade of gray by one as one bit out of N bits of the gray shade registers.
Also, a preferable mode is one wherein the AND of specified low order bits of the color data is computed and, when the ANDed value is zero (0), the color data is judged to be the intermediate gray shade.
According to a third aspect of the present invention, there is provided a method of displaying gray shades comprising the steps of:
deciding color data corresponding to given image data by using the color data determining means;
providing a display pattern corresponding to the color data by using the pattern recognizing means;
deciding gray shade data providing a specified shade of gray by giving frame rate control to the color data by using the frame rate controlling means; and
deciding whether an intermediate gray shade is displayed or not by using the extension register provided within the pattern recognizing means.
According to a fourth aspect of the present invention, there is provided a method of displaying gray shades comprising the steps of:
deciding color data corresponding to given image data by using the color data determining means;
providing a display pattern corresponding to the color data by using the pattern recognizing means;
deciding gray shade data providing a specified shade of gray by giving frame rate control to the color data by using the frame rate controlling means; and
deciding whether an intermediate gray shade is displayed or not by using the extension register provided within the frame rate controlling means.
In the foregoing, it is preferable that it is provided with N gray shade registers each providing a different display pattern and wherein an intermediate gray shade is displayed in N shades of gray by using data of the gray shade register providing a higher shade of gray by one as one bit out of N bits of gray shade registers.
Also, it is preferable that the AND of specified low order bits of the color data is computed and, when the ANDed value is zero (0), the color data is judged to be the intermediate gray shade.